1. Field of the Invention
The present invention relates to a color image reproduction system for reproducing a target color image (colors) using an image output device such as a color printer, a color copying machine, a color facsimile device, a color monitor, or the like and, more particularly, to a color image reproduction system having a color analysis function which allows conversion processing reflecting the characteristics of an image output device.
Also, the present invention relates to a color image reproduction system having a data transmission function which can accurately reproduce a color image in consideration of the characteristics of a color image output device even when a location where the colors of a target color image (colors) are colorimetrically measured is distant from the location of the image output device.
2. Description of the Related Art
In recent years, the uses of color image output devices such as a color printer, a color copying machine, a color facsimile device, a liquid crystal color display, a color CRT display, a projection type color display, and the like have been widespread.
Normally, the above-mentioned color image output devices represent various colors using three primary colors. When colors are to be artificially represented, different colors are assigned to a plurality of sub-area regions which are independent of each other or partially overlap each other in a very small area for representing a single color. A target color is recognized by a mixing of these colors in the visual sense of man.
This technique includes the subtractive color mixing process and the additive color mixing process. For example, in the subtractive color mixing process, three primary colors, i.e., C (cyan), M (magenta), and Y (yellow), and K (black) are used, whereas in the additive color mixing process, three primary colors, i.e., R (red), G (green), and B (blue) are used. In correspondence with the ratios of these primary colors, a color recognizable by man is determined. In this manner, a color is represented using ratios of the primary colors, and values corresponding to the ratios of the primary colors will be referred to as color separation values hereinafter. A color image signal used in the color image output device normally represents the above-mentioned CMY- or RGB-based color separation values, and such a color image signal will be referred to as a color separation value signal hereinafter.
As one problem related to color separation value signals, the above-mentioned values corresponding to the ratios of the primary colors are values which vary depending on the characteristics of each specific image output device, i.e., device-dependent values. The characteristics of the image output device are features defined by the image output method, the print material to be used, and the like. Therefore, the fact, that the device-dependent color separation value signals are device dependent, means that output color tones vary depending on factors such as the type of color image output device to be used, the color output method, the print materials (pigments, dyes, and the like) to be used in a print operation even when an identical color image signal is input. If different output devices are caused to output the same color, the color separation values must be changed in correspondence with the characteristics of the respective output devices. Therefore, in order to reproduce the same color, color separation value signals for overlapping dots such as CMY(K) signals, RGB signals, and the like must be generated in correspondence with the output devices involved.
For example, with the development of personal computers, design can be made with the use of a personal computer, and a color printer, or the like can be used as an output device. Furthermore, as a design step, coloring or creation of color samples is often performed. The fact that a target color cannot always be accurately output is a considerable obstacle to a designer.
On the other hand, as a device for quantitatively analyzing a color, a colorimetric device is known. According to this colorimetric device, when the colors of an input color sample are measured, colorimetric values such as CIE L*a*b* values, XYZ values, and the like of the color sample can be obtained. Color systems of the colorimetric values such as the CIE L*a*b* (to be referred to as L*a*b* hereinafter) values, XYZ values, and the like of display colors by numerical values, and are represented in the form of sets of three numerical values.
The L*a*b* color system is one recommended by the CIE (Commission Internationale de I'Eclairage) in 1976, and is a uniform color space which is defined so that a predetermined distance between two colors displayed on this coordinate system corresponds to a predetermined perceptive color difference in any color region. An L* value represents the degree of lightness of a color, and a combination of a* and b* values represent the relationship between the hue and saturation of a color.
The XYZ color system is one associated with data of a standard observer adopted by the CIE in 1931, and is defined by tristimulus values calculated using color matching functions x(.lambda.), y(.lambda.), and z(.lambda.). Values (colorimetric values) defined in these spaces are the values of colors themselves which are independent of the characteristics of input/output devices, i.e., device-independent values.
In this manner, the colorimetric values represent, as numerical values, the lightness, hue, and saturation; in the L*a*b* colorimetric system, L represents the lightness, a represents the hue, and b represents the saturation; and in the XYZ colorimetric system, x and y represent the chromaticity (hue and saturation), and Y represents the lightness. These numerical values are indices for objectively and quantitatively representing colors. The same colorimetric values express the same colors independently of the color materials, the output method, and the like.
However, signals of the colorimetric values defined by the L*a*b* or XYZ color system cannot be directly used in an image output device such as a color printer. For this reason, it is very difficult to cause a color image output device to be used to output a color to be represented.
A color image output device such as a color printer, a copying machine, a color facsimile device, or the like is often used as a plain color proof machine in the field of process printing. In these busy times, it is often difficult to assure a staff meeting time, and a design center is often distant from a print factory. For this reason, a designer may want to send a design sample to staffs, or to give a color instruction to a distant party.
In order to meet such demand, a conventional transmission technique may be used, and transmitted data may be output by a color image output device. However, as described above, since the color separation values which are transmitted by the conventional transmission technique are values depending on the characteristics of an output device, desired colors cannot always be properly reproduced.